Control system



H. S. OGDEN CONTROL SYSTEM Filed Oct. 11, 1939 Inventor Harold S. O

J 9d n, a by is Kt torney.

Patented Oct. 7, 1941 CONTROL SYSTEM Harold S. Ogden, Erie, Pa., assignor to General Electric Company, a corporation of New York Application October 11, 1939, Serial No. 298,956

12 Claims.

My invention relates to control systems for electric motors, more particularly to systems for controlling the acceleration of single-phase alternating current railway motors of the type using preventive coil and a buck-boost transformer means for obtaining various voltage steps, and has for its object a simple and reliable means for preventing momentary sag or decrease in the tractive effort of the motor while the voltage connections are being changed.

In accordance with my invention, I connect the buck-boost transformer across the preventive coil and I connect also across the preventive coil a suitable resistance during the interval in which the connections are being changed between the preventive coil and the different voltage taps on the supply transformer.

I also connect the resistor across the exciting winding of the buck-boost transformer during the interval that the buck-boost transformer is being switched independently of the preventive coil.

For a more complete understanding of my invention, reference should be had to the accompanying drawing, Fig. l of which is a diagrammatic representation of an alternating current railway motor control system embodying my invention; Fig. 2 is a sequence chart for various positions of the switches or contactors; while Fig. 3 is a simplified diagram of connections during the transfer from one tap connection on the main transformer to the next.

Referring to the drawing, I have shown my invention in one form as applied to the control of a single-phase alternating current series motor l provided with an exciting field winding l l, a compensating field winding l2 and an interpole field winding l3. The motor is energized from taps on the secondary winding l4 of a supply transformer having a primary winding l5. As shown, the primary winding I5 has one terminal connected to a suitable alternating current source such as a trolley wire by means of a trolley l6 and its other terminal connected to a ground ll.

As shown, four terminals or taps only are provided on the secondary windin l4 although, of course, more may be'provided if desired. However, by means of an iron core preventive coil l8 and an iron core buck-boost transformer IS a multiplicity of voltages are obtained from the four transformer taps. As shown, the lower tap or terminal of the transformer secondary winding is connected directly to one side of the motor.

The connections between the three upper taps of the secondary winding I4 and the preventive coil l8 are controlled by electromagnetically operated switches or contactors 20 to 25 inclusive. Also the connections between one of the windings 26 of the buck-boost transformer l9 and the preventive coil are controlled by two switches 21 and 28. Thus with the two switches 21 and 28 in their uppermost or lowermost positions the winding 26 is connected with one polarity or the other across the preventive coil, but with one of the switches 21 or 28 in its upper position and the other in its lower position, the winding 26 is short circuit/ed.

Also I have provided a suitable impedance shown as a resistor 29 which may be connected across the winding 26 by a switch 30.

A manually operated druin'controller 3! is provided for suitably controlling the tap switches 20 to 25, the reversing switches 21 and 28 and the switch 30 to control the speed of the motor. In its first position, the controller energizes from a suitable auxiliary control supply source, shown as a storage battery 32, a coil 3la which closes the starting switch32a in the motor circuit. Also energized in this position are the coils 33 and 34 which close their switches 20 and 2|. These last-mentioned two switches connect both terminals of the preventive coil l8 to the same tap 35 of the transformer and, consequently, the voltage of the tap 35 is applied to the motor circuit. Also, in the first position of the controller 3|, the coils 36 and 36:: are energized whereby the switches 21 and 28 are lifted to their uppermost positions to connect the coil 26 with a predetermined polarity across the preventive coil l8. At this time, however, since the preventive coil is short circuited by the switches 20 and 2|, no voltage is applied to the coil 26 and the voltage of tap 35 is the voltage applied to the motor.

A suitable relay interlocking system is provided for the coils of the switches. The coil 33 is energized through a switch 31 operated by a coil 38 which is directly energized from the controller 3!. Also the coil 38 closes a switch 39 which closes a holding circuit for the coil 38 through a relay switch 40 to the conductor 4| leading to the upper contact of the controller 3| and connected through the conductors of the controller and the lower controller contact to one side of the battery 32. The circuit of the coil 33 also includes normally closed interlock switches 42, 43, 44 and 45 which are connected to the switches 22 to 25 inclusive.

The coil 34 is similarly energized through a switch 46 operated by a coil 41. In a similar manner this coil 41 closes a switch 48 in a holding circuit for itself. leading through an interlock switch 49. The coil 34 is interlocked through the switches 43, 44 and 45.

It is believed that the connections and operation of the coils 58, 5|, 52 and 53 will be clear from the preceding description with the help of the sequence chart. Thus in the second position of the controller 3| with the switch 20 open the switch 2! closed and the switch 22 closed, the

preventive coil 15 is connected across the transformer taps 55 and 55 so as to give a voltage halfway between these taps which voltage is reduced for the motor by the action of the buck-boost transformer i9.

In position 3 of the controller 3], the coil 36 is deenergized whereby the switch 21 drops to its lower position and short circuits the buck-boost coil 25. This gives a motor voltage half-way between the taps 35 and 55, the buck-boost transformer being inactive.

In position 5 the coil 35a is deenergized whereby the switch 28 drops to its lower position thus connecting the coil 25 across the preventive coil l8 with a polarity which is reversed with respect to its polarity in position 2. This causes the buck-boost transformer to boost the transformer voltage.

In the flith position of the controller, the coil 34 is deenergized and the switch 2| opens while the coil 5| is energized to close the switch 23. The opening of the switch 2| also deenergizes the buck-boost transformer coil 25. At this time the motor is supplied with the full voltage of the tap 54.

It is believed that the connections established in the remaining positions of the controller 3| will be clear from the preceding description.

For the purpose of assuring a predetermined momentary closure of the switch 30 to connect the resistor 28 across the coil 25 between the various positions of the controller 3| a coil 55 is provided which is energized momentarily between positions by the controller contacts 55. This coil closes a switch 51 which energizes the coil 58 for the resistor switch 50. Also the coil 55 closes an interlock switch 55 which establishes a holding circuit for the coil 55 through the relay switch 50 held closed by its coil 5|. It will be observed that the coil BI is energized through a normally closed switch 62 operated by the coil 58. Also the coil Bl closes a switch 53 to short circuit the resistance 65 in the circuit of the coil 55 whereby the coil is given a tremendous pick-up force. Preferably the coil 55 is wound for continuous operation on a lower voltage than that of the supply source 32 to obtain increased pickup force.

When the coil 58 closes the switch 30 and opens the switch 52, the coil 6| is deenergized and the switch 60 opens after a time interval determined by the inherent operating time of coil 61 (requires time to open its contacts) or of a timing device Sla to deenergize the coil 55. The coil 55 then releases its switch 51 which drops open and deenergizes the coil 58 to again open the switch 30. In the event that the controller is held in a mid-position, it will be observed that the deenergization of the coil 6| and opening of the switch 63 inserts the resistance 64 in circuit with the coil 55 to prevent overheating of the coil. This interlocking arrangement assures the momentary closure of the switch 30 when the controller 31 is moved rapidly from one position to the next.

It will be observed that the switches 21, 28 and iii are controlled to connect the buck-boost transformer coil 26 and the resistor 29 in parallel with each other across the preventive coil l8 during the time that the preventive coil i8 is open circuited and one terminal only connected to a transformer tap. This condition occurs when the controller 3| is moved between positions |-2, l-5, 5-6, and 8-9. Thus, when the controller 31 is moved from the fourth position to the fifth position, the switch 21 is first opened which leaves the upper half only of the preventive coil 18 connected through the switch 22 to the transformer tap 54. This upper half of the preventive coil, unless means were provided to prevent it, would momentarily under these conditions introduce an appreciable reactance voltage drop in the motor circuit whereby the voltage applied to the motor would be correspondingly reduced. This is undesirable because of the resulting irregular and jerky operation of the motor by reason of its momentarily reduced voltage and torque.

With the resistor and coil 25 connected in parallel with the preventive coil, however, in accordance with my invention, the motor current divides equally between the preventive coil on the one hand and the resistor and winding 25 on the other hand. As shown diagrammatically in Fig. 3, indicating the momentary conditions existing in passing from the fourth to the fifth position of the controller 3|, one-half of the motor current passes through the upper half of the preventive coil, as indicated by the arrow 55a, while the other half of the motor current passes through the lower half of the preventive coil, as indicated by the arrow 64b. This latter half 01 the motor current divides equally between the resistor 29 and th winding 25, the preventive coil acting as an autotransformer. This division of motor Current is brought about by using a 4:1 transformer l9 whereby its primary winding 25 has one-fourth motor current induced in it, and by using a resistance 29 of such value that it will not have a voltage across it high enough to saturate or over-excite the preventive coil and buckboost transformer. As a result of this action, the currents in the upper and lower halves of the preventive coil flowing in opposite directions inductively neutralize each other so that substantially no inductive voltage drop appears across the preventive coil. Therefore, no decrease in the motor voltage takes place during the momentary existence of this condition.

When the switches 21 and 25 are operated independently of the switches 20 to 25 inclusive, by controller movement between positions 2-3, 34, 6-7, and 1-8, the resistor 25 is connected across the winding 25 of the buck-boost transformer momentarily during the interval in which the switch 21 or 28 is open and the winding 25 is thereby open-circuited. The resistor 29 is thus connected across the winding 25 so that the current induced in the winding 25 by the primary winding 26a exactly neutralizes the ampere turns of the winding 26a. The value of the resistor is such as to practically short-circuit the winding 26. This prevents any appreciable impedance drop across the winding 25a during these intervals and thereby prevents resulting momentary sag or decrease in motor voltage and at the same time prevents excessive voltages being induced in winding 26.

Additional interlock means is provided by the relay interlock switches operated by the coils 55 and 66. When the coil 65 is deenergized and its interlock switches 40, 10 and H thereby closed, these interlock switches assure respectively that any one of the coils 38, i2 and 13 which may be energized when these switches close is maintained closed by a holding circuit through its interlock switch respectively and, therefore, cannot be opened so long as the coil 55 is deenergized, by movement of the controller II to any operating position. These coils control the group of p Switches 22 and 24, which control the connection of the upper terminal of the preventive coil to the transformer taps. Likewise, when the coil 66 is deenergized and its interlock switches 49, 14 and 16 are closed, these switches respectively establish a holding circuit for any one of the coils 41, I6 and 11 that may then be energized. Consequently, these coils operating the group of tap switches 2|, 23 and 25 cannot be deenergized by the controller 3| so long as these interlock switches remain closed. This means that the tap switches 20 to 26 inclusive, which are closed respectively when the coils 68, 41, 12, 16, 13 and 11 are energized, cannot be opened by the movement of the controller 3i to any other Operating position when the coils 66 and 66 are deenergized. In other words, the tap connections remain as they are until one or the other of the coils 66 or 66 is energized.

The coils 65 and 66 are energized from the conductor 4| through a common interlock switch 6'l operated by the coil 58. In addition, the coil 65 is energized through two normally open interlock switches 68 and 69 operated by the coils 36 and 36a while the coil 66 is energized through two normally closed interlock switches 18 and I6 operated by the coils 36 and 36a.

In this manner, the tap switch combinations are interlocked with the switches 21, 28 and 30. A tap switch combination existing before the controller 3| is moved is maintained until the switches 21, 26 and 30 assume their proper positions for the next tap change. Thus, a tap switch change cannot be made until, first the switch 30 is closed to close the interlock switch 61 which closure of the switch 30 is effected by movement of the controller 3! between steps and, second, a tap switch change can be made only when the switches 21 and 28 are in their positions to give the correct polarity of the winding 26 as connected to the preventive coil l8, this latter interlocking previously noted being effected by the interlock switches 68, 69 and I8, 19. It will be noted, for example, from the sequence chart, Fig. 2, that in the positions 4, and 6, the tap switches 2|, 23 and 25 are closed and opened in sequence, this being possible because the coil 66 is energized between steps or positions of the controller 36. At this same time, however, the coil 65 is deenergized continuously.

Short circuits across sections of the transformer winding l4 and the possibility of the application of overvoltage to the preventive coal are prevented by the normally closed interlock switches 42, 43, 44, 45, 80, BI, 82, 83 and 84. For example, it will be observed that the coil 33 cannot be energized if any one of the tap switches H to 25 inclusive is closed which might cause a short circuit or overvoltage condition. The closure of each tap switch opens its corresponding interlock switch referred to above.

While I have shown a particular embodiment of my invention, it will be understood of course that I do not wish to be limited thereto since many modifications may be made and I therefore contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A motor control system comprising a supply transformer having a plurality'of voltage taps, a preventive coil, two groups of tap switches for connecting respectively the terminals of said preventive coil to selected ones of said taps, a buckboost transformer having a winding arranged for connection in a motor circuit and a second winding inductively associated with said first winding, reversing switches for, connecting said second winding across said preventive coil, said switches being normally in positions to connect said second winding across said preventive coil for one polarity and movable to second positions for reversed polarity, means operated by movement of said reversing switches to one of said positions for maintaining closed a predetermined group of said tap switches, means operated by movement of said reversing switches to said normal positions for maintaining closed the other of said groups of tap switches, and interlocking means between the tap switches of each group preventing the closure of more than one of the switches of each group at any one time.

2. A motor control system comprising a supply transformer having a plurality of voltage taps, a preventive coil, two groups of normally open electromagnetic tap switches operable to connect respectively the terminals of said preventive coil to selected ones of said voltage taps, a buck-boost transformer having a winding arranged for connection in a motor circuit and a second winding inductively associated with said first winding, electromagnetically operated reversing switches for connecting said second winding across said preventive coil, a resistor, a normally open electromagneticallycperated resistor switch for connecting said resistor across said second winding of said buck-boost transformer, a controller movable to a plurality of positions to control said switches, and means selectively operated by said reversing switches and said resistor switch for holding closed one of said tap switches of one of said groups independently of said controller and for opening said one tap switch upon operation of said resistor switch and said reversing switches to other positions.

3. A motor control system comprising a supply transformer having a plurality of voltage taps, a preventive coil, two groups of tap switches for connecting respectively the terminals of said preventive coil to selected ones of said taps, a buckboost transformer having a winding arranged for connection in a motor circuit and a second winding inductively associated with said first winding, reversing switches for connecting said second winding across said preventive coil, said switches being normally in positions to connect said second winding acrosssaid preventive coil for one polarity and movable to second positions for reversed polarity, interlock means operated by movement of said reversing switches to each of said positions for maintaining closed a predetermined group of said tap switches, interlock means between the tap switches of each group preventing the closure of more than one of the switches of each group at any one time, a resistor, resistor switching means for connecting said resistor across said second winding, and switching means operated by said resistor switching means for operating said interlock means to release said predetermined group of tap switches.

4. A motor control system comprising a supply transformer having a plurality of voltage taps, a preventive coil, two groups of tap switches for connecting respectively the terminals of said preventive coil to selected ones of said taps, a buckboost transformer having a winding arranged for connection in a motor circuit and a second winding inductively associated with said first winding, reversing switches for connecting said second winding across said preventive coil, said iii.

switches being normally in positions to connect said second winding across said preventive coil for one polarity and movable to second positions for reversed polarity, a resistor, resistor switch ing means for connecting said resistor across said second winding, a controller movable to predetermined positions to control said tap and reversing switching means and to close said resistor switching means in moving from one of said positions to another, interlock means operated by movement of said reversing switches to each position for maintaining closed a predetermined group of said tap switches independently of movement of said controller while providing for selective operation of the other group of said tap switches by said controller, means operated by said resistor switching mean for disabling said interlock means, and interlock means between the tap switches of each group preventing the closure of more than one of the switches of each group at any one time.

5. A motor control system comprising a supply transformer having a plurality of voltage taps, a preventive coil, two groups of normally open electromagnetic tap switches operable to connect respectively the terminals of said preventive coil to selected ones of said voltage taps, a controller movable to a plurality of predetermined positions selectively to clos said tap switches, normally closed holding switches in holding circuit for said tap switches, a coil for opening said holding switches for the tap switches of each group, a buck-boost transformer having a winding arranged for connection in a motor circuit and a second winding inductively associated with said first winding, two electromagnetically operated reversing switches for connecting said second winding across said preventive coil, said controller being arranged to operate said reversing switches in conjunction with said tap switches, a normally closed interlock switch operated by each of said reversing switches, connections connecting said normally closed interlock switches in series with each other in the circuit of one of said coils, a normally open interlock switch operated by each of said reversing switches, and connections connecting said normally open interlock switches in series with each other in the circuit of the other of said coils.

6. A motor control system comprising a supply transformer having a plurality of voltage taps, a preventive coil, two groups of normally open electromagnetic tap switches operable to connect respectively the terminals of said preventive coil to selected ones of said voltage taps, a controller movable to a pluralityof predetermined positions selectively to close said tap switches, normally closed holding switches in holding circuits for said tap switches, a coil for opening said holding switches for the tap switches of each group, a buck-boost transformer having a winding ar ranged for connection in a motor circuit and a second winding inductively associated with said first winding, two electromagnetically operated reversing switches for connecting said second winding across said preventive coil, switching means operated by said reversing switches connected in circuits with said coils, said controller being arranged to operate said reversing switches in conjunction with said tap switches, a resistor, a normally open electromagnetically operated resistor switch for connecting said resistor across said second winding of said buck-boost trans former, a normally open interlock switch operated with said resistor switch connected in circuit with both of said coils, and means including said controller for operating momentarily said resistor switch to its closed position between said predetermined positions.

7. A motor control system comprising a supply transformer having a plurality of voltage taps, a preventive coil, two groups of normally open electromagnetic tap switches operable to connect respectively the terminals of said preventive coil to selected ones of said voltage taps, a controller movable to a plurality of predetermined positions selectively to close said tap switches, normally closed holding switches in holding circuits for said tap switches, a coil for opening said holding switches for the tap switches of each group, a buck-boost transformer having a winding arranged for connection in a motor circuit and a second winding inductively associated with said first winding, two electromagnetically operated reversing switches for connecting said second winding across said preventive coil, said switches being in normally closed positions to connect said second winding across said preventive coil for one polarity and movable to a second position for reversed polarity, said controller being arranged to operate said reversing switches in conjunction with said tap switches, a normally closed interlock switch operated by each oi said reversing switches, connections connecting said normally closed interlock switches in series with each other in the circuit of one of said coils, a normally open interlock switch operated by each of said reversing switches, connections connecting said normally open interlock switches in series with each other in the circuit of the other of said coils, a resistor, a normally open electromagnetically operated resistor switch for con necting said resistor across said second winding of said buck-boost transformer, a normally open interlock switch operated with said resistor switch connected in circuit with both of said coils, and means including said controller for operating momentarily said resistor switch to its closed position between said predetermined positions.

8. A control system comprising a supply transformer having a plurality of different voltage taps, a preventive coil provided with two end terminals and with a substantially central tap dividing said preventiv coil into two portions, tap switching means for connecting in one position the said terminals of said preventive coil to a selected pair of said taps, a transformer having a winding arranged for connection in a motor circuit and a second winding inductively associated therewith, reversing switching means for connecting in one position said second winding across said preventive coil with one polarity and movable to short-circuit said second winding and to connect said second winding across said preventive coil with reversed polarity, said reversing switching means open circuiting said second winding in moving from one position to another to effect each change in its connections, an impedance, normally open impedance switching means movable to a closed position to connect said impedance across said second winding, and a controller having a plurality of positions for controlling said tap switching means, and for controlling said reversing switching means and said impedance switching means to connect said impedance across said second winding during the time interval that said second winding is open circuited by said reversing switching means and then open said impedance switching means after said reversing switching means has operated either to connect said second winding across said preventive coil or to short-circuit said second winding.

9. A control system comprising a supply transformer having a plurality of different voltage taps, a preventive coil provided with two end terminals and with a substantially central tap dividing said preventive coil into two portions, tap switching means for connecting in one position the said terminals of said preventive coil to a selected pair of said taps and movable to disconnect one of said terminals from said supply transformer and then connect said one terminal to a different one of said taps, a transformer having a winding arranged for connection in a motor circuit and a second winding inductively associated therewith, reversing switching means for connecting in one position said second winding across said preventive coil with one polarity and movable to disconnect said second winding from said preventive coil and connect said second winding across said preventive coil with reversed polarity, a resistor. resistor switching means for connecting said resistor across said second winding, a controller having a plurality of first positions for controlling said tap switching means to connect said preventive coil selectively to diil'erent taps, and means on said controller between said first positions for controlling said reversing switching means and said resistor switching means to connect both said second winding and said resistor across said preventive coil during the time interval that one terminal of said preventive coil is disconnected from said supply transformer. 10. A control system comprising a supply transformer having a plurality of different voltage taps, a preventive coil provided with two end terminals and with a substantially central tap dividing said preventive coil into two portions, tap switching means for connecting in one position the said terminals of said preventive coil to a selected par .of said taps and movable to disconnect one of said terminals from said supply transformer and then connect said one terminal to a different one of said taps, abuck-boost transformer having a secondary winding arranged for connection in a motor circuit and a primary winding inductively associated there with, reversing switching means for connecting one position said primary winding across said preventive coil with one polarity and movable to short-circuit said primary winding and-to connect said primary winding across said preventive coil with reversed polarity, said reversing switching means disconnecting at least one terminal of said primary winding from said preventive coil and thereby open circuiting said primary winding in effecting each change in the connections of said primary winding, a resistor, resistor switchingmeans for connecting said resistor across said primary winding, and a controller having a plurality of positions for sequentially controlling said switching means to connect said preventive coil selectively to different taps, to connect both said primary winding and said resistor across said preventive coil during the time interval that one terminal of said preventive coil is disconnected from said supply transformer and to connect said resistor across saidprimary winding when said primary winding is open circuited, said buck-boost transformer having a ratio between its windings to provide when one for substantially one-fourth motor current in said primary winding and for substantially equal currents in said two portions of said preventive coil.

11. A control system comprising a supply transformer having a plurality of different voltage taps, a preventive coil provided with two end terminals and with a substantially central tap dividing said preventive coil into two portions, tap switching means for connecting in one position the said terminals of said preventive coil to a selected pair of said taps, a transformer having a winding arranged for connection in a motor circuit and a second winding inductively associated therewith, a first reversing switch biased to one closed position to connect a first end of said second winding to a: first terminal of said preventive coil and movable to a second closed position to connect said first end of said second winding to the second terminal of said preventive coil, a second reversing switch biased to one closed position to connect the second end of said second winding to the second terminal of said preventive coil and movable to a second closed position to connect said second end of said second coil to said first terminal of said preventive coil, an impedance, impedance switching means for connecting said impedance across said second winding, and a controller for selectively controlling said reversing switching means and said impedance switching means to connect said impedance across said second winding during the time interval that each one, of said reversing switches is open while moving from one closed position to another.

12. A control system comprising a supply transformer having a plurality of different voltage taps, a preventive coil provided with two end terminals and with a substantially central tap dividing said preventive coil into two portions, tap switching means for connecting in one position the said terminals of said preventive coil to a selected pair of said taps and movable to disconnect one of said terminals from said supply transformer and then connect said one terminal to a different one of said taps, a buck-boost transformer having a winding arranged for connection in a motor circuit and a second winding inductively associated therewith, a first reversing switch biased to one closed position to connect a first end of said second winding to a first terminal of said preventive coil and movable to terminal of said preventive coil is disconnected 7 0nd end of said second winding to the second terminal of said preventive coil and movable to a second closed position to connect said second end of said second coil to said first terminal of said preventive coil, an impedance, impedance switching means biased to an open position and movable to a closed position to connect said impedance across said second winding, and a controller having a plurality of positions for selectively controlling said switching means to connect said preventive coil selectively to difierent ones of said taps, to connect said second winding across said preventive coil, to short-circuit said second winding, and to connect said impedance across said second winding during the time in terval that each of said reversing switches is open while moving from one closed position to another,

HAROLD S. OGDENr 

